1. Field of the Invention
This invention relates to a crankcase for an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine mounted in a vehicle such as an automobile, blow-by gas treatment for returning gas containing fuel to an intake passages, because the gas containing fuel leaks from a combustion chamber to a crankcase through a space between a cylinder inner wall and a piston ring (blow-by gas) during the operation of the internal combustion engine.
When the blow-by gas that leaks from the combustion chamber to the crankcase is returned to the intake passage by means of the blow-by gas treatment, this blow-by gas flows into a gas outflow passage extending in a vertical direction from the crankcase to a cylinder block of the internal combustion engine, and reaches the intake passage via the gas outflow passage. When the blow-by gas passes through the gas outflow passage extending in the vertical direction, the oil contained in the blow-by gas separates from the gas by using the self-weight of the oil, and the remaining blow-by gas without the oil is returned to the intake passage. The oil separated from the blow-by gas in the gas outflow passage, on the other hand, is returned from the gas outflow passage into the crankcase.
Moreover, it is considered that the gas outflow passage can be connected to an oil separator described in, for example, Japanese Patent Application Publication No. 2006-336595 (JP-A-2006-336595) (paragraphs [0015], [0016], [0018], and [0024], for example), in order to separate the oil from the blow-by gas more effectively. This oil separator introduces the blow-by gas from the gas outflow passage and adheres the oil contained in the gas to a separation wall by abutting the flow of the gas against the separation wall, in order to separate the oil from the gas. In this case, because the blow-by gas from which the oil is separated as the blow-by gas passes through the gas outflow passage is further separated from the oil by the oil separator and returned to the intake passage, the oil can be separated from the blow-by gas more effectively. Note that the oil that is separated from the blow-by gas by the oil separator is also returned from the gas outflow passage into the crankcase.
As described above, the oil can be separated effectively from the blow-by gas that is returned to the intake passage, by separating the oil from the blow-by gas by means of the gas outflow passage or oil separator. However, it is preferred that the oil be separated as much as possible from the blow-by gas that is returned to the intake passage, and the oil needs to be separated from the gas more effectively.